The present invention relates to an optical pickup for optical disks, and more particularly to an optical pickup having a movable part equipped with an objective lens, a laser diode and photodetectors.
In recent years, optical storage media, such as a compact disc (CD) and a digital versatile disk (DVD), are rapidly becoming in widespread use. An optical pickup is usually used as a device that performs a read from and a write onto such an optical storage medium.
FIG. 7 shows a construction of a conventional optical pickup 400 in a longitudinal cross-sectional view. As shown in FIG. 7, the optical pickup 400 has a movable part 406 which is equipped with an objective lens 401 and coils 405. A fixed part supports the movable part 406 almost horizontally via four wires 421 which are positioned in parallel to one another. The fixed part 407 is fixed onto an optical base 409.
Since FIG. 7 is the longitudinal cross-sectional view obtained by vertically cutting the optical pickup 400, two out of the four wires 421 are not shown in FIG. 7. In addition to the fixed part 407, the optical base 409 is equipped with: a yoke 410 holing a magnet 411; an integrated component 402; a collimator lens 420; and a mirror 403. The integrated component 402 contains a semiconductor laser and photodetectors. The semiconductor laser emits a laser beam, which is then collimated by the collimating lens 420 to generate a collimated beam, and an optical path is changed by 90° with the mirror 403. The beam enters the objective lens 401, which then focuses the beam onto the storage surface of an optical storage medium 412. The beam is then reflected on the surface of the storage medium, and reverses along the above optical path. The photodetectors in the integrated component 402 detects this beam, so that a signal recorded on the storage medium 412 can be read by the optical pickup 400.
Optical storage media tend to vertically vibrate when they are rotated. Therefore, the objective lens 401 has to be moved along the optical axis so that the storage surface of the optical storage medium 412 is always located in the depth of field of laser beam L1 converged by the objective lens 401. Besides, eccentricities in the rotation of the optical storage medium 412 make it also necessary to reposition the laser beam L1 so that it correctly follows a track on the optical storage medium 412. Accordingly, an optical pickup is required to have an adjusting function and an error detecting function for having the laser beam correctly focused on the storage medium, and for having the laser beam correctly follow a track.
Therefore, the photodetector in the integrated component 402 detects a focusing error and a tracking error by receiving the return light, and suitably controls currents supplied to the coils 450. Lorenz forces, generated by the magnetic field of the magnet 411 attached to the yoke 410 and the current going through the coils 405, move the objective lens 401 in a focusing direction and a tracking direction. As a result, the optical pickup 400 can accurately perform a write onto and a read from the optical storage medium 412.
However, in the optical pickup that uses the above-described conventional objective lens driver, the integrated component 402, collimator lens 420 and mirror 403 are fixed over the optical base 409, and only the objective lens 401 is moved so as to adjust the focus position and follow the track. Therefore, a displacement is generated between the chief rays of the laser beam emitted from the semiconductor laser and the optical axis of the objective lens 401. Due to this displacement, in the conventional optical pickup shown in FIG. 7, a lens aberration, a reduction in RIM strength or the like are generated. As a result, precision of the optical pickup 400 for a write onto and a read from the optical storage medium 412 decreases. Herein, both the accuracy of writing the information storage signal to the optical storage medium and that of reading the information storage signal to the optical storage medium will be collectively and simply called “optical reading accuracy”.
In order to solve the above-described problems, not only an objective lens but also a semiconductor laser and photodetectors are mounted in a moving part so that the positional relationship of these optical components is always fixed, thereby preventing optical displacements. The optical pickup including the moving part equipped with a plurality of optical elements as described above will be herein called an “integrated optical pickup”.
The present inventors have already disclosed an exemplary integrated optical pickup, such as one described above, in Japanese Unexamined Patent Publication No. 2001-344783. This integrated optical pickup includes a movable part equipped with optical elements such as a semiconductor laser and an objective lens, and the movable part is supported by a fixed part via a plurality of supporting members in a manner that allows the movable part to move in both the focusing and the tracking directions. Furthermore, in this optical pickup, at least two of the plurality of supporting members are conductive in order to supply drive currents to the semiconductor laser.
This integrated optical pickup prevents the displacement, and therefore, the optical characteristic of this optical pickup is improved as compared with the optical pickup shown in FIG. 7.